The recent emergence of second-generation, third-generation and higher wireless communication systems creates a need for wireless communication devices capable of accessing multiple communication systems with different radio access technologies within one or more wireless frequency bands. For example, the emergence of various communications standards has driven the need for wireless communication devices, such as wireless telephones, and other types of wireless devices, to be capable of accessing multiple communication systems employing different radio access technologies such as, for example, a global system for mobile communications (GSM) and wideband code division multiple access (W-CDMA) communication systems serving a common geographical area. The multimode wireless communication device may be, for example, a wireless phone, two-way radio, computer equipped with a wireless modem, wireless personal data assistants (PDAs), Internet compliance data terminal or any other suitable device. Having multimode capability allows a wireless device to operate with wireless communication systems having different modulation modes.
The full exploitation of the services of multiple communication systems using different radio access technologies in the same frequency band requires that the multimode wireless devices operate simultaneously on more than one communication system while tolerating interference caused by other transmitters on both systems without significant performance degradation. Since the bandwidth of each wireless frequency band, such as the United States 800 MHz and 1900 MHz wireless communication bands, and the 900 MHz and 1800 MHz wireless communication bands in Europe are fixed, as multiple modulation modes are permitted to transmit within the same frequency band, each multimode wireless transceiver and each base station must tolerate even greater levels of interference than if a single modulation mode in a frequency band is required. Further, as the number of multimode wireless devices communicating in a wireless communication system increases, system interference also generally increases. Interference is caused by other transmitters such as wireless devices and base stations transmitting on either the same frequency channel (co-channel), adjacent frequency channels, or any other frequency channel. As a result, new techniques are required in order to compensate for the interference caused by transmitters on a same or a different frequency with the same or different modulation modes.
For example, according to one embodiment, the multimode wireless transceiver has the capability to receive and transmit in two different modes such as in GSM and W-CDMA. This allows a user to move from one system to another, as long as the multimode wireless transceiver supports the standard for the system in operation. According to this example, both receivers in the multimode wireless transceiver may be required to contend with cross modulation interference caused in part by one of the transmitters within the multimode wireless transceiver transmitting a transmit signal, which is a well known interference phenomenon. Examples of the types of interference signals are second order intermodulation product signals, and third order intermodulation product signals including cross modulation. The second and third order interference product signal frequencies are related to the sum and difference products of the harmonics of two or more interference blocker signals generated in a device, such as in an amplifier or a receiver circuit, due to nonlinear characteristics inherent in the device. One set of second order interference product signals relate to the sum and difference products of at least two interference blocker signal frequencies, such as one signal frequency denoted by F1, and a second signal frequency denoted by F2, such that the sum product is F1+F2 and the difference product is denoted by F1−F2. Another set of second order interference product signals relate to simple square law detection of the envelope of a single interference signal at either F1 or F2 that may fall within the frequency band of interest. One set of third order harmonic interference product signal frequencies of importance are (2·F1−F2) and (2·F2−F1) that fall within the frequency band of interest. Another set of third order harmonic interference product signal frequencies of importance involve the crossmodulation of the transceiver transmitter spectrum onto an interference signal at either F1 or F2 such that the transmitter spectrum falls within the frequency band of interest.
According to one method in a single receiver wireless device, the linearity or spurious free dynamic range of a receiver stage such as a low noise amplifier (LNA) stage of the receiver, may be improved in order to reduce the generation of third order interference product signals as is known in the art. However, since only one receiver is used during normal operation, the single receiver wireless device cannot simultaneously receive a wireless signal and detect an interference blocking signal causing the generation of the interference product signal. Additionally, increasing the linearity or spurious free dynamic range of the LNA increases power consumption within the wireless device. Such a technique does not seek to reduce the generation of third order interference products within the receiver by other techniques that do not increase power consumption. Accordingly, such a method is limited to increasing the linearity or spurious free dynamic range of the low noise amplifier in a single receiver wireless device. This same reasoning can be applied to other devices in the receiver such as mixers, baseband amplifiers, baseband filters, and analog to digital converters.
According to another method, a multimode wireless transceiver includes two receivers to receive two wireless signals of different modulation modes in a non-concurrent method of operation. However, one receiver does not simultaneously receive a wireless signal while the other receiver detects a blocking interference source. Further, such a multimode wireless transceiver cannot operate simultaneously to receive a wireless signal while the second receiver detects the blocking interference source without causing a degradation of performance in one or the other receiver.